In the refrigerant circuit of vehicle air conditioning systems, refrigerant undergoes changes of state in a closed circulatory process, for which purpose at least two heat exchangers are required. At a first heat exchanger (refrigerant cooler, refrigerant condenser), heat is extracted from the gaseous refrigerant (after it has been compressed and heated by a compressor), and at the second heat exchanger (evaporator) heat is supplied from outside to the refrigerant as it evaporates. Air flowing past the evaporator can thus be cooled and air flowing past the refrigerant condenser can be heated.
The air which is supplied to the passenger cabin for cooling or conditioning the latter is conducted to the evaporator, cooled there and then conducted into the passenger cabin. In this case, the evaporator is usually arranged in an air distributor duct connected to the outlet of a blower and leading into the passenger cabin, whereas the other components of the air conditioning system are accommodated outside the passenger cabin.
A certain fraction of oil is admixed to the refrigerant for the purpose of lubricating the compressor. In the event of leakage or damage to a component of the refrigerating circuit and/or to the refrigerant lines connected to the components, refrigerant and therefore the admixed oil may escape.